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GFS2: Take glock reference in examine_bucket() 

We need to check the glock ref counter in a race free way
in order to ensure that the gfs2_glock_hold() call will
succeed. The easiest way to do that is to simply take the
reference count early in the common code of examine_bucket,
skipping any glocks with zero ref count.

That means that the examiner functions all need to put their
reference on the glock once they've performed their function.

Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>
Reported-by: David Teigland <teigland@redhat.com>
Tested-by: David Teigland <teigland@redhat.com>
This commit is contained in:
Steven Whitehouse 2013-08-20 09:35:09 +01:00
parent 7c0ef28a2c
commit 7286b31eab
1 changed files with 5 additions and 7 deletions
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12
fs/gfs2/glock.c
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@ -1488,7 +1488,7 @@ static void examine_bucket(glock_examiner examiner, const struct gfs2_sbd *sdp,
rcu_read_lock();
hlist_bl_for_each_entry_rcu(gl, pos, head, gl_list) {
if ((gl->gl_sbd == sdp) && atomic_read(&gl->gl_ref))
if ((gl->gl_sbd == sdp) && atomic_inc_not_zero(&gl->gl_ref))
examiner(gl);
}
rcu_read_unlock();
@ -1508,18 +1508,17 @@ static void glock_hash_walk(glock_examiner examiner, const struct gfs2_sbd *sdp)
* thaw_glock - thaw out a glock which has an unprocessed reply waiting
* @gl: The glock to thaw
*
* N.B. When we freeze a glock, we leave a ref to the glock outstanding,
* so this has to result in the ref count being dropped by one.
*/
static void thaw_glock(struct gfs2_glock *gl)
{
if (!test_and_clear_bit(GLF_FROZEN, &gl->gl_flags))
return;
goto out;
set_bit(GLF_REPLY_PENDING, &gl->gl_flags);
gfs2_glock_hold(gl);
if (queue_delayed_work(glock_workqueue, &gl->gl_work, 0) == 0)
if (queue_delayed_work(glock_workqueue, &gl->gl_work, 0) == 0) {
out:
gfs2_glock_put(gl);
}
}
/**
@ -1536,7 +1535,6 @@ static void clear_glock(struct gfs2_glock *gl)
if (gl->gl_state != LM_ST_UNLOCKED)
handle_callback(gl, LM_ST_UNLOCKED, 0, false);
spin_unlock(&gl->gl_spin);
gfs2_glock_hold(gl);
if (queue_delayed_work(glock_workqueue, &gl->gl_work, 0) == 0)
gfs2_glock_put(gl);
}